Black poop is usually caused by something you ate, drank, or took as a supplement. Iron pills, bismuth-based stomach medicines, black licorice, blueberries, and blood sausage can all turn your stool dark or black. In most of these cases, the color change is harmless and temporary. However, black stool can also signal bleeding in your upper digestive tract, which needs medical attention. The key is knowing how to tell the difference.
Foods and Supplements That Turn Stool Black
Several everyday items can change your stool color without any cause for concern. Iron supplements are one of the most common culprits. Black or very dark stool is a normal, expected side effect of oral iron tablets. Activated charcoal supplements do the same thing.
Certain foods are also responsible. Black licorice (the real kind, made with licorice extract), blueberries, and blood sausage can all darken your stool noticeably. Beets and red-dyed foods sometimes produce dark reddish-brown stool that can look black in dim bathroom lighting.
Bismuth-based over-the-counter stomach medicines, like Pepto-Bismol, are another frequent cause. The bismuth in these products reacts with small amounts of sulfur naturally present in your saliva and digestive system. That reaction creates bismuth sulfide, a black compound that discolors both your tongue and your stool. It’s completely harmless.
If any of these are the cause, your stool color should return to normal within a couple of days after you stop taking the supplement or eating the food in question.
How to Tell If It’s Blood
When black stool comes from bleeding in the upper digestive tract (the stomach, esophagus, or the first section of the small intestine), it has a medical name: melena. Melena looks and feels different from stool that’s simply been stained by food or medication, and the differences are recognizable.
Classic melena is jet black with a tarry, sticky consistency. It clings and smears rather than holding a normal shape. The most distinctive feature is the smell. Melena has a particularly strong, foul odor that’s noticeably worse than typical stool. That smell comes from blood being broken down and digested as it moves through your GI tract. The longer the blood has traveled, the darker and more pungent it becomes. A small amount of bleeding may look more dark brown than truly black, and if the bleeding also triggers diarrhea, the stool can be wetter and looser than the classic tarry description.
Stool that’s been darkened by food or bismuth won’t have that same distinctive smell. It also tends to have a more normal texture and consistency. If you’re unsure, think about what you’ve eaten or taken in the past day or two. If nothing on the list of common causes applies and the stool is sticky, tarry, or unusually foul-smelling, that’s a signal worth acting on.
What Causes Bleeding in the Upper GI Tract
The most common cause of melena is a peptic ulcer, which is an open sore in the lining of the stomach or the upper small intestine. These ulcers can bleed slowly or quickly depending on their size and depth. Gastritis (inflammation of the stomach lining) is another frequent source. Both conditions are often caused by a bacterial infection or long-term use of anti-inflammatory painkillers like ibuprofen or aspirin.
Less common but more serious causes include tears in the esophagus, abnormal blood vessels in the digestive tract, and tumors. Alcohol-related liver disease can cause swollen veins in the esophagus that are prone to bleeding. In any of these cases, the blood is partially digested before it exits the body, which is what turns it black rather than red.
Symptoms That Appear Alongside Serious Bleeding
Black, tarry stool from internal bleeding rarely shows up in isolation. People with significant upper GI bleeding often experience abdominal pain, lightheadedness, dizziness, or fainting. Some also vomit blood, which may look bright red or resemble dark coffee grounds depending on how long it’s been in the stomach. A rapid heart rate and a drop in blood pressure are signs that a meaningful amount of blood has been lost.
If you’re seeing black, tarry stool along with any of these symptoms, that combination points to active bleeding that needs emergency evaluation. Even without other symptoms, persistent tarry black stool that you can’t explain by diet or medication warrants a call to your doctor.
How Doctors Check for Blood in Stool
If your doctor suspects bleeding but it’s not visually obvious, they may order a fecal occult blood test. This test detects tiny amounts of blood that are invisible to the naked eye. There are two main types. A fecal immunochemical test (FIT) is generally preferred because it’s more sensitive and doesn’t require any dietary changes beforehand. A guaiac-based test is older and typically requires you to collect samples from three separate bowel movements.
These tests can only confirm whether blood is present or absent. They can’t identify where the bleeding is coming from. A positive result could mean anything from a stomach ulcer to a polyp to a nosebleed you swallowed. If the test comes back positive, the next step is usually a colonoscopy or an upper endoscopy, which lets doctors look directly at the lining of your digestive tract to find the source.
It’s also worth knowing that these tests aren’t perfect. A negative result doesn’t guarantee there’s no problem, since some bleeding is intermittent. And a positive result doesn’t automatically mean something serious is wrong.
A Simple Way to Think About It
Start by reviewing what you’ve eaten or taken in the last 48 hours. Iron supplements, Pepto-Bismol, activated charcoal, black licorice, and blueberries are the most common harmless explanations. If one of those fits, stop taking or eating it and see if your stool returns to its normal brown within a day or two.
If none of those apply, pay attention to the stool’s texture and smell. Normal-textured, non-sticky, non-foul stool that happens to be dark is far less concerning than the classic tarry, sticky, strongly odorous presentation of melena. And if the black stool comes with abdominal pain, dizziness, vomiting, or a racing heartbeat, treat it as urgent.